The present invention relates to a surface mount optical coupler, a method of mounting the same, and a method of producing the same. More specifically, the present invention relates to a surface mount optical coupler using a silicon substrate.
In a surface mount optical coupler, components such as an optical semiconductor device and an optical part are precisely mounted at specific positions on a silicon substrate through image recognition or mechanical positioning. In a method of mounting an optical semiconductor device and an optical part, an axis adjusting process for adjusting axes thereof to achieve optical coupling is omitted or simplified (refer to Patent References 1 and 2).
With reference to FIGS. 9(A), 9(B), and 10, conventional surface mount optical couplers will be explained. FIGS. 9(A) and 9(B) are views showing a configuration of the conventional surface mount optical coupler. As shown in FIGS. 9(A) and 9(B), the conventional surface mount optical coupler includes an optical semiconductor device 10 and an optical fiber 60 as an optical part.
In a method of producing the conventional surface mount optical coupler, a V-shaped groove 14 is formed in a surface of a silicon substrate 12 through an alkali etching process. The optical semiconductor device 10 (laser diode or photo diode) is precisely mounted at a specific position on the silicon substrate 12 through image recognition or mechanical positioning. A pigtail bare fiber 16 is placed in the V-shaped groove 14 such that a distance between an end surface of the optical fiber 60 and a light emitting surface or a light receiving surface of the optical semiconductor device 10 becomes a proper optical coupling distance, thereby forming the conventional surface mount optical coupler.
Accordingly, in the method of producing the conventional surface mount optical coupler, it is possible to mount the optical semiconductor device 10 and the optical fiber 60 without an axis adjusting process. That is, when a resin layer of the optical fiber 60 at a distal end portion thereof is removed through a bare process of the pigtail bare fiber 16, the distal end portion of the optical fiber 60 becomes a bare optical fiber in a state that a glass portion thereof is exposed.
In general, the pigtail bare fiber 16 has a very small amount of decentration with respect to an outer diameter of a bare fiber and a core center. Accordingly, when the pigtail bare fiber 16 is placed in the V-shaped groove 14, it is possible to precisely position the pigtail bare fiber 16 with respect to the optical semiconductor device 10 mounted precisely (refer to Patent Reference 3).
In the optical fiber 60, a cover cord 18 covering the bare optical fiber is reinforced with a flexible plastic or an ultraviolet setting resin. Accordingly, it is possible to increase strength of the optical fiber 60 and improve handling performance thereof while the base optical fiber is still flexible.
After an intermediate assembly of the conventional surface mount optical coupler is placed in a package 20, the package 20 is air-tightly sealed, thereby obtaining the conventional surface mount optical coupler. In this process, an Au metal portion 22 deposited in advance on the pigtail bare fiber 16 is inserted into a metal pipe 24. Afterward, the metal pipe 24 is sealed with sealing solder 26, and a cover 28 is welded to the package 20.
When the conventional surface mount optical coupler is attached to an electrical circuit board, package leads 30 are connected to the electrical circuit board with solder, so that an excess amount of heat is not conducted to the cover cord 18.
FIG. 10 is a view showing another conventional surface mount optical coupler. The conventional surface mount optical coupler shown in FIG. 10 has a configuration of a collimator lens coupling type. In the conventional surface mount optical coupler, a collimator lens 32 converts divergent light emitted from the optical semiconductor device 10 (laser diode) mounted on the silicon substrate 12 to parallel light. A collective lens 34 converges the parallel light one more time and couples to the pigtail bare fiber 16 (refer to Patent Reference 4).
In the conventional surface mount optical coupler shown in FIG. 10, a space between the collimator lens 32 and the collective lens 34 is used for mounting an isolator and the likes. The pigtail bare fiber 16 is mechanically positioned in the V-shaped groove 14. Further, the collimator lens 32 and the collective lens 34 are mounted in lens mounting V-shaped grooves 36 formed in the silicon substrate 12 without an axis adjusting process. Accordingly, it is possible to significantly simplify the axis adjusting process of the optical part.    Patent Reference 1: Japanese Patent Publication No. 11-6941    Patent Reference 2: Japanese Patent Publication No. 2003-344711    Patent Reference 3: Japanese Patent Publication No. 2005-55475    Patent Reference 4: Japanese Patent Publication No. 2001-94191
In the conventional surface mount optical coupler described above and shown in FIGS. 9(A) and 9(B), when the surface mount optical coupler is placed in the package 20, it is necessary to deposit the Au metal portion 22 on the pigtail bare fiber 16, so that the outlet portion of the optical fiber 60 is sealed with the sealing solder 26. Further, it is necessary to provide the metal pipe 24 in a sidewall of the package 20 for inserting the pigtail bare fiber 16, thereby increasing processing cost.
In the conventional surface mount optical coupler described above and shown in FIGS. 9(A) and 9(B), it may be possible to seal the outlet portion of the optical fiber 60 with a resin, or to use a less expensive plastic package. In this case, however, although it is possible to reduce cost, it is difficult to air-tightly seal the package 20 and to achieve necessary reliability, thereby making it difficult to balance cost and performance.
Further, when the conventional surface mount optical coupler is attached to the electrical circuit board, it is difficult to stably place the package 20 on the electrical circuit board due to a repulsive force of the optical fiber 60. As a result, it is difficult to attach the conventional surface mount optical coupler to the electrical circuit board with solder using a soldering iron.
All of the other electric components are mounted on the electrical circuit board through a reflow process. Accordingly, if it is possible to mount the conventional surface mount optical coupler through the reflow process, it is possible to significantly improve efficiency of the mounting operation.
However, in the reflow process, it is necessary to heat a component up to 230 to 250° C. that exceeds a withstand temperature of the cover cord 18. Further, it is difficult to stably place the conventional surface mount optical coupler on the electrical circuit board. As a result, in general, the conventional surface mount optical coupler is attached to the electrical circuit board with solder using a soldering iron.
In the surface mount optical coupler of the collimator lens coupling type shown in FIG. 10, in order to correct mode mismatching between the laser diode and the optical fiber, it is necessary to convert (image enlargement) a spot image of the laser diode through a lens to a size substantially same as that of the optical fiber. However, it is difficult to completely correct the mode mismatching, thereby lowering coupling efficiency.
Further, in the conventional surface mount optical coupler of the collimator lens coupling type, it is necessary to achieve high angle tolerance between the lenses. Accordingly, it is necessary to mount the laser diode and the lenses with high accuracy. Therefore, when the laser diode and the lenses are mounted without an axis adjusting process, production yield tends to lower.
In view of the problems described above, an object of the present invention is to provide a surface mount optical coupler with low cost and improved reliability. Further, an object of the present invention is to provide a method of mounting the surface mount optical coupler and a method of producing the surface mount optical coupler with improved efficiency.
Further objects and advantages of the invention will be apparent from the following description of the invention.